The internet of communicating things in a smart city
Stephen Hawking once said: “For millions of years, mankind lived just like the animals. Then something happened which unleashed the power of our imagination. We learned to talk.” A similar revolutionary leap is currently taking place in technology. Technologies are learning to communicate. As a result, new analytical possibilities, processes and solutions have arisen. The boundaries of our imagination have been further expanded.
The world today depends on communication canals. The development of communication technologies is extremely fast, constantly having to respond to the newest demands. One of the driving forces behind these innovations is the Internet of Things (IoT), a platform that allows to exchange measured values and communicate remote commands between technologies that used to operate on their own. Now we can see cars communicating with car parks, soil moisture meters with expert systems that transmit data to combine harvesters, or a fridge in the kitchen communicating with a shopping list in a mobile phone.
In modern cities, one can stumble upon IoT technologies at almost every corner. However, it raises the following question: how could we ensure a high-quality data transmission in such an exposed environment that cities undoubtedly are, where the transfer often has to be carried out wirelessly? When examining possible solutions, it is important to take into account the following criteria:
- How much data do we want to send?
- How often?
- What power source will the transmitter/receiver use?
- What is the desired range?
- What kind of topology will the network use? (star/mesh)
- How noisy is the environment where the communication is supposed to take place?
- Will the transmitter be mobile?
A weather station mounted on a street lamp pole, a camera monitoring the traffic, or a medical alert bracelet with a ‘help’ button on a pensioner’s wrist all present different communication demands. Depending on our answers, we can currently choose from the following communication technologies:
The most widely used technology in households and public spaces today is undoubtedly WiFi. This seasoned, constantly improving technology is suitable wherever a big volume of data from various devices – such as consumer electronics like mobile phones or tablets – is to be transmitted in a reliable way. However, its disadvantages include its high transmission power overloading the end instrument and its limited signal range (typically not more than hundreds of metres in an open area). This is why we rarely see simple or single-purpose devices using WiFi. On the other hand, what WiFi lacks in range it makes up in speed and data flow. We can see today the first implementations of WiFi mesh networks which could lead to new application possibilities and a broader deployment in the future. An interesting example of area-wide WiFi coverage can be seen in Barcelona. (http://ajuntament.barcelona.cat/barcelonawifi/en/).
3G/4G GSM networks
These were the first massively deployed wireless communication technologies. In cities, their absolute advantage consists in their reliability of transfer, coverage and a wide portfolio of devices. Devices communicating via GSM/GPRS are becoming a valuable source of information for systems evaluating the traffic, for instance. Without us knowing it, mobile phones share information about the traffic with services such as Google Maps or Waze. The disadvantage that many hope and expect will soon be eliminated is that these networks require a SIM card, which rules out certain areas of application where SIM cards cannot be used – for example because of space requirements.
Originally a French technology, SigFox is probably the world’s fastest growing IoT operator today, with a presence in 60 countries. It was mainly designed to ensure simple and quick communication between sensory devices within their wireless network. Some of SigFox’s advantages are its good coverage in Slovakia and its low cost of data transfer and communication modules. Its disadvantages are related to its use of the free unlicensed band 868 MHz, and include a potentially noisy environment and the 1% band utilisation limit. The latter means that it is only possible to transfer 1% of the time, so if transmitting a message lasts 2 seconds, in the next 2 x 99 = 198 seconds the device cannot transmit any data. The size of one SigFox message is 12 bytes, which is enough to transmit information like the GPS location and the speed of a device. This should be sufficient for the majority of parameters that are measured in a smart city.
Besides SigFox, it is probably the most widely used WAN (wide area network) in Europe. However, unlike SigFox it does not only have one operator, meaning that anyone can build their own LoRaWAN network according to their needs; this, however, also means that they have to maintain it on their own. This technology is often the preferred choice for water, gas or electricity meters within a single area or a bigger building. LoRaWAN also enables energy-efficient two-way communication, thanks to which a simple sensor equipped with a small battery can send data up to 10 years. Similarly to SigFox, LoRaWAN also has a good signal range, which is the reason why it is frequently used in hard-to-reach areas with no GSM signal.
NB-IoT is often seen as the technology that will eliminate most of the shortcomings its current rivals suffer from. However, its biggest problem is its limited deployment thus far, meaning that we do not have sufficient information about its application in the real environment. This technology depends on 4G coverage and will mainly be used by established Telcos which already have an infrastructure. We can therefore expect good indoor and outdoor coverage. According to its specification, NB-IoT should operate faster than LoRa(WAN) and offer a better QoS (quality of service). In the near future, the development of this technology will certainly merit attention.
Bluetooth/Bluetooth Low Energy
Similarly to WiFi it is a widely used technology. Every smartphone today is equipped with a Bluetooth chip. It was specifically designed for short-range communication. However, Bluetooth should not be confused with BLE (Bluetooth Low Energy). While traditional Bluetooth was primarily developed for continuous data transfer e.g. sound transmission in wireless earphones, BLE focuses on low-energy data transmission in devices that are designed to run on a battery for several years. It is typically used in the so-called beacons, i.e. small transmitters that continuously transmit messages. After installing the necessary mobile application, BLE can help to navigate in a shopping centre, monitor the number of visitors, or can be used to measure a room’s temperature or carbon dioxide level. BLE is also be used in so-called wearables such as fitness bracelets. These are equipped with miniature batteries and can function for several days or weeks on a single charge.
This wireless technology merits special attention because it differs from the others in a substantial way. It uses the so-called energy-harvesting technologies, which allow it to operate without cable, battery or other power supply. It draws energy from its environment via solar panels (light), thermoelectric panels (heat) or mechanical switches (kinetic energy). This way it does not suffer from the shortcoming present in its rivals: the need for regular battery changing. The EnOcean technology is especially suitable for use in buildings, for which they offer the widest range of products. The most interesting of these are thermostatic heads drawing energy from radiators, or window handles that after being turned charge the electronic devices and send a signal to the control system that the window is open.
A Czech technology whose validity is proved by its alliance with companies such as Zyxel, AAEON and Intel. The advantage of this wireless technology – similarly to BLE, ZigBee and Zwave – consists in its ability to operate in the so-called mesh network (see D!ossier). Although there has not yet been a massive expansion of this low-energy technology, we can already see some interesting applications such as collecting the occupancy of car parks from in-door sensors or monitoring.
ZigBee is undoubtedly one of the most popular wireless technologies for indoor usage. Numerous manufacturers have adapted this technique, including Philips with its lighting system HUE, or IKEA with its TRÅDFRI devices. It also has an industrial application e.g. in smart metering. This technology uses mesh networks and has low power consumption thanks to its sleep mode, which the device can enter in certain circumstances and therefore conserve the battery.
Implementation companies sometimes offer solutions based on proprietary communication protocols – that is protocols that are usually developed by a single manufacturer and are incompatible with each other, or need protocol converters to achieve interoperability. While this is a welcome trait in a home security system with a wireless control, IoT devices generally avoid using such technologies as it is difficult – or nearly impossible – to integrate them into larger functional units.
Combining multiple communication protocols
Some application areas may benefit from using multiple communication protocols. Take fill-level sensors installed in waste containers, for example. Typically, every sensor in a bin enclosure sends its measured data to the master module, which serves as a data concentrator. To establish communication, the sensors use the energy-efficient Bluetooth Low Energy protocol. The master module then collects this data and forwards it via another communication protocol e.g. GSM or SigFox. This method’s main advantage is its optimisation of output communication costs.
The power consumption of wireless technologies
There are cases when sensors are installed in hard-to-reach areas, or when frequent battery change is seen as unwanted as it increases maintenance costs. In consequence, when looking for the right technology, it is important to take into consideration how the following factors impact battery life:
- Data transmission frequency
- The device’s attenuation mode
- Transmission signal strength
A different data transmission frequency is required from a smart water consumption meter or when measuring, for example quarter-hour maximum electricity consumption. On the other hand, a weather station deployed in the city centre enhanced with a dust sensor, or NOx or Sox emission sensors, may only transfer data when they exceed the limit values. Many single-purpose sensor manufacturers add a sleep function to their devices which keeps the sensor in low-power mode, wakes it up once per a set period of time (e.g. 4 hours), and then communicates the recently measured data. Some wireless communication technologies make it possible to modify the transmission performance level, which has a direct impact on power consumption.
Mesh networks versus star topology networks
Communication networks usually use star topology, i.e. they have one main transmitter/receiver that acts as a conduit and transmits messages between all the components of the network (examples include WiFi, GSM, SigFox etc.). However, in certain areas of deployment, mesh networks are becoming increasingly frequent. These are network whose participants – the so-called nodes – exchange data directly, while they are also able to forward the messages of their ‘neighbouring’ nodes. Therefore, the range – and often the robustness – of the network increases with the number of nodes participating in it. However, mesh may not be the ideal choice for long-distance communication, as it may require the use of plenty of nodes, automatically leading to slower data transmission. To ensure the optimal communication path, the correct placing of a node is another aspect to be taken into consideration when designing and building a network.